Perpendicular magnetic recoding head with a laminated pole

ABSTRACT

A laminated write pole layer for a PMR write head is disclosed in which a plurality of “n” magnetic layers and “n−1” non-magnetic spacers are formed in an alternating fashion on a substrate. The non-magnetic spacers promote exchange decoupling or antiferromagnetic coupling between adjacent magnetic layers. Writability is improved when the trailing magnetic layer has a thickness greater than the thickness of other magnetic layers and preferably &gt;25% of the total thickness of the magnetic layers. The thicknesses of the other magnetic layers may be equal or may become progressively smaller with increasing distance from the trailing magnetic layer. In another embodiment, the non-magnetic spacer between the trailing magnetic layer and the nearest magnetic layer is replaced by a magnetic spacer made of a soft magnetic material to promote magnetic coupling and effectively increase the thickness of the trailing magnetic layer.

This is a Divisional application of U.S. patent application Ser. No.11/879,952, filed on Jul. 19, 2007, which is herein incorporated byreference in its entirety, and assigned to a common assignee.

RELATED PATENT APPLICATIONS

This application is related to Headway Docket #HT07-013, Ser.#11/825,034, filing date Jul. 3, 2007; and Headway Docket #HT07-005,Ser. #11/820,962, filing date Jun. 21, 2007; both assigned to the sameassignee as the current invention and which are herein incorporated byreference in their entirety.

FIELD OF THE INVENTION

The invention relates to a main pole layer of a PMR writer and a methodfor making the same wherein the main pole layer is a laminate of amagnetic material and a non-magnetic spacer to improve overwriteperformance, minimize data erasure after a write operation, and improvesignal to noise ratio.

BACKGROUND OF THE INVENTION

Perpendicular magnetic recording (PMR) has become the mainstreamtechnology for disk drive applications beyond 200 Gbit/in², replacinglongitudinal magnetic recording (LMR) devices. Due to the continuingreduction of transducer size, high moment soft magnetic thin films witha Bs above 22 kG are required for write head applications. A PMR headwhich combines the features of a single pole writer and a double layeredmedia has a great advantage over LMR in providing higher write field,better read back signal, and potentially much higher areal density. Inparticular, a shielded pole head can provide a large head field gradientat the trailing side due to the presence of a trailing shield andsubstantially improve the write performance. However, PMR still sufferssome problems. One of the biggest issues is the head-induced dataerasure that is of particular concern since the erasure occurs afterwriting. This type of erasure is believed to be caused by a remanentmagnetization in the main pole layer and is also related to the sharppointed geometry of the write pole.

A conventional PMR write head as depicted in FIG. 1 typically has a mainpole layer 10 or write pole with a pole tip 10 t at an air bearingsurface (ABS) 5 and a flux return pole (opposing pole) 8 which ismagnetically coupled to the write pole through a trailing shield 7.Magnetic flux in the write pole layer 10 is generated by coils 6 andpasses through the pole tip into a magnetic recording media 4 and thenback to the write head by entering the flux return pole 8. The writepole concentrates magnetic flux so that the magnetic field at the writepole tip 10 t at the ABS is high enough to switch magnetizations in therecording media 4. A trailing shield 7 is added to improve the fieldgradient in the down-track direction.

Referring to FIG. 2, a top view is shown of a typical main pole layer 10that has a large, wide portion called a yoke 10 m and a narrowrectangular portion 10 p called a pole that extends a neck height (NH)distance y from the ABS plane 5-5 to a plane 3-3 parallel to the ABSwhere the pole intersects the yoke at the neck 12. The main pole layer10 flares outward at an angle θ from a dashed line 11 that is anextension of one of the long rectangular sides of the pole 10 p. PMRtechnologies require the pole 10 p at the ABS to have a beveled shape(as viewed from the ABS) so that the skew related writing errors can besuppressed.

In the fabrication process, the yoke 10 m and pole 10 p may be formed bypatterning a photoresist layer (not shown) above an alumina layer andthen transferring the pattern through the alumina by an etching processto form a mold. An electroplating process or sputter deposition methodmay be used to deposit a main pole layer 10 that fills the cavity in thealumina. Finally, a lapping process is employed to remove the end of thepole 10 p opposite the yoke 10 m and thereby define an ABS plane 5-5.

Laminating a write pole layer and main pole is shown to improve theerase-after-write problem by Y. Okada, et al. in “Magnetic properties ofFeCo multilayered films for single pole heads”, IEE Trans. Magn., Vol.40, No. 4, pp. 2368-2370 (July 2004). Anti-ferromagnetic coupling wasobserved between 25 nm thick FeCo layers and 1 nm thick Cr layers, and[FeCo/Cr]_(n) multilayered configurations helped stabilize the pole.

Slonczewski et al. in “Micromagnetics of laminated permalloy films”,IEEE Trans. on Magn., Vol. 24, No. 3, pp. 2045-2053 (May 1998), reportthat lamination may be used to eliminate closure-domain walls fromcertain shapes of practical interest. In one example, two permalloyfilms each 1.6 microns thick in the main pole layer are separated by anon-magnetic layer that is 12 nm thick.

In other prior art, U.S. Pat. No. 6,950,277 discloses a write pole thathas a thin downstream magnetic layer having lower saturationmagnetization and a thicker upstream magnetic layer with highersaturation magnetization that is designed to straighten the write fieldcontour of the pole tip.

In U.S. Pat. No. 6,243,939, a first pole layer made of NiFe or CoFeNi isseparated from a second pole layer made of the same material by a writegap layer that has a high ion beam etch rate to prevent erosion of thesecond pole layer during a trimming step.

U.S. Pat. No. 6,233,116 teaches a laminated write pole in which 500 to600 Angstrom thick layers of high moment magnetic material such as FeRhNare separated by a 100 to 200 Angstrom thick amorphous alloy layer suchas CoZrCr. In this case, both types of layers are magnetic to improveoverall permeability and uniaxial anisotropy in the high momentmaterial. However, magnetic remanence is not improved.

In U.S. Pat. No. 5,379,172, a magnetic head with upper and lower poletips having a laminated structure comprised of NiPX alloy layers andNiFe layers is described. The layers on the ends of the lamination havea thickness of D while the middle layers have a thickness of 2D.

U.S. Pat. No. 7,120,988 describes a method of forming a write pole witha trailing shield. The write pole is laminated with magnetic layers(CoFe, NiFe, or CoFe/NiFe) and non-magnetic layers of Rh, Ru, or Cr.There is no description of the relative thickness of the layers but adrawing suggests essentially the same thickness for each laminatedlayer.

A laminated high moment film involving an antiferromagnetic couplingscheme with Ru coupling layers between high moment layers has beendescribed in U.S. Pat. No. 7,057,853 and by Y. Chen et al. in “Highmoment materials and fabrication processes for shielded perpendicularwrite head beyond 200 Gb/in²”, IEEE Trans. Magn. Vol 43, No. 2, p 609(2007). In the laminated scheme, a high moment material such as a FeColayer is laminated into several thinner FeCo layers that are separatedby non-magnetic layer insertions. When a non-magnetic laminationmaterial such as Ru, Rh, or Cr reaches a certain thickness, a couplingenergy is generated such that the magnetization of the FeCo layers oneither side of a Ru or non-magnetic layer will align in anti-paralleldirections thereby establishing an anti-ferromagnetic (AFC) laminatedconfiguration. Since the magnetization in a FeCo layer is orientedopposite to that of the magnetic moment in the nearest FeCo layer, theremanent magnetization can be reduced.

One disadvantage of prior art AFC lamination schemes is that thecoupling strength of a FeCo/Ru/FeCo configuration or the like istypically large and this type of AFC lamination will inevitably cause alarge anisotropy field and low magnetic moment under a low field.Although the coupling strength can be lowered by using a thickernon-magnetic layer (increasing Ru thickness from 7.5 to about 18Angstroms, for example), the magnetic moment will be diluted as thenon-magnetic content in the FeCo/Ru/FeCo stack is increased. Therefore,an improved lamination scheme for a write pole is needed that enables ahigh magnetic moment while simultaneously providing a mechanism toreduce remanence.

SUMMARY OF THE INVENTION

One objective of the present invention is to provide a laminated mainpole layer with high moment material that provides good overwriteperformance, and has a design that reduces remanence so that poleerasure is minimized in PMR writer applications.

Another objective of the present invention is to provide a laminatedmain pole layer according to the first objective while providing a meansto improve signal to noise ratio.

A third objective of the present invention is to provide a method forforming a laminated main pole layer according to the first twoobjectives that is compatible with current manufacturing process flowsand equipment.

These objectives are realized in the present invention by firstproviding a substrate upon which a write pole and main pole layer may beformed. In one embodiment, an etch stop layer may be formed on thesubstrate followed by forming an insulation layer on the etch stoplayer. A mold for the main pole layer is formed in the insulation layerby a sequence of photoresist imaging and etching steps. In one aspect, aphotoresist layer is coated on the insulation layer and patternwiseexposed to form an opening in the shape of a main pole layer with yokeand write pole sections that uncovers a portion of the insulation layer.Thereafter, the opening is transferred through the insulation layer by areactive ion etch (RIE) process that stops on the etch stop layer.Optionally, the mold formation sequence may include a first photoresistpatterning and etching sequence followed by a second photoresistpatterning and etching sequence to define different portions of theopening that correspond to different sections of the main pole layer.

After the photoresist layer is removed, a seed layer may be deposited onthe insulation layer and on the etch stop layer within the mold shape.Then a series of sputter deposition steps are performed to fabricate themain pole layer within the mold shape. A key feature is that the mainpole layer has a laminated structure comprised of a magnetic layer (M)such as FeCo or FeCoNi and a non-magnetic spacer (S) such as Ru or Al₂O₃to give a [M/S]_(n)/M configuration where n is an integer. Preferably, athickness for the non-magnetic spacer is selected so that each magneticlayer is exchange decoupled or anti-ferromagnetically coupled throughthe non-magnetic spacer. Furthermore, the thickness of the magneticlayer on the trailing side of the laminated structure is made thickerthan the other magnetic layers. In one aspect, when the trailingmagnetic layer has a concave shape with a curved trailing edge, thevolume of trailing magnetic layer is preferably greater than 25% of thetotal magnetic layer volume in the laminated write pole structure. Whenthe trailing magnetic layer has a flat trailing edge, then the thicknessof the trailing magnetic layer is preferably greater than 25% of thetotal thickness of the magnetic layers.

In one embodiment, the other magnetic layers in the laminated structurehave essentially the same thickness which is less than the thickness ofthe trailing magnetic layer. Alternatively, the thickness of eachsuccessive magnetic layer becomes greater from leading edge to trailingedge in the laminated structure and the trailing magnetic layerthickness comprises at least 25% of the total thickness of all magneticlayers. In a third embodiment, there is a magnetic spacer between thetrailing magnetic layer and the adjacent magnetic layer while anon-magnetic spacer is employed between other magnetic layers in thelaminated structure. After the laminated main pole layer is formed, oneor more annealing processes such as hard axis annealing, easy axisannealing, or combinations of both hard axis and easy axis annealing maybe employed. Then a planarization process such as a chemical mechanicalpolish (CMP) step may be performed to make the top surface of thelaminated main pole layer coplanar with the adjacent insulation layer.

The present invention also anticipates that a laminated write pole layermay be formed by a photoresist patterning and etching process thatincludes an ion beam etch or the like. For example, a photoresist layermay be patterned in the shape of a main pole layer including a writepole on the stack of laminated layers on a substrate to provide an etchmask such that a subsequent etch removes portions of the laminated stacknot protected by the etch mask. Once the photoresist mask is removed, aninsulation layer is deposited on and adjacent to the patterned writepole and main pole layer and then in a subsequent planarization step,the insulation layer is made coplanar with the write pole and main polelayer.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a conventional PMR writer showingthe main write pole, flux return pole, magnetic recording media, andcoils that generate magnetic flux.

FIG. 2 is a top view showing a main write pole layer of a conventionalPMR write head that has a narrow write pole section adjacent to the ABSand a larger yoke section with sides that flare outward at an angle θfrom the sides of the narrow write pole.

FIG. 3 is a graph that shows the remanent field decreases as the numberof laminated magnetic layers with equal thickness in a conventionalwrite pole increases.

FIG. 4 is a graph that shows the write field in a down-track positiondecreases as the number of laminated layers with equal thickness in aconventional write pole increases.

FIG. 5 is a graph that shows the write field at the trailing edgedecreases as the thickness of the non-magnetic spacer layers increasesin a conventional write pole.

FIG. 6 a is a top view that depicts the magnetic flux near the writepole tip in a single layer pole, and FIG. 6 b is a top view that showsthe magnetic flux in a conventional laminated write pole near the ABSplane.

FIG. 7 is a graph that depicts overwrite capability as a function of thenumber of magnetic layers having equal thickness in a conventionallaminated write pole.

FIG. 8 a is a cross-sectional view from an ABS plane of a write poleformed within an insulation layer according to an embodiment of thepresent invention, and FIG. 8 b is an enlarged section of the write polein FIG. 8 a that shows a laminated structure of thicker magnetic layersand thinner non-magnetic layers in which the trailing magnetic layer islarger than the other magnetic layers in the write pole.

FIG. 9 a is a top view of a laminated write pole according to a firstembodiment of the present invention in which there is a thick trailingmagnetic layer having a greater thickness than other magnetic layerswhich are equal in size.

FIG. 9 b is a top view of a laminated write pole according to a secondembodiment of the present invention in which there is a thick trailingmagnetic layer and other magnetic layers in the laminated structurebecome progressively thinner with increasing distance from the trailingmagnetic layer.

FIG. 9 c is a top view of a third embodiment of the present inventionwherein there is a magnetic spacer between the trailing layer and thelayer adjacent to the trailing layer, and other magnetic layers areseparated by a non-magnetic spacer.

FIG. 10 is a top view of a laminated write pole according to the presentinvention that depicts the magnetic flux within the various magneticlayers of the laminated structure.

FIGS. 11 a-11 d are top views of various configurations of a laminatedwrite pole in which the trailing magnetic layer becomes progressivelythicker from FIG. 11 a to FIG. 11 d while the remaining magnetic layersare equivalent in size and the total lamination thickness is constant.

FIG. 12 a and FIG. 12 b are graphs that depict the write field as afunction of down track position for the various laminated configurationsin FIGS. 11 a-11 d.

FIG. 13 is a graph showing write field at the trailing edge as afunction of the trailing magnetic layer thickness ratio for thelaminated configurations in FIGS. 11 a-11 d.

FIG. 14 is a graph showing the overwrite capability as a function of thetrailing magnetic layer thickness ratio for the laminated configurationsin FIGS. 11 a-11 d.

FIG. 15 is a graph showing transition length as a function of thetrailing magnetic layer thickness ratio for the laminated configurationsin FIGS. 11 a-11 d.

DETAILED DESCRIPTION OF THE INVENTION

The present invention is a laminated main pole layer formed in a PMRwriter and a method of making the same. Although the exemplaryembodiments describe a main pole layer in which both the write pole andyoke are laminated, the present invention also anticipates embodimentswherein the write pole is laminated and at least a portion of the mainpole layer is not laminated. In addition, the main pole layer may have astitched pole structure. Furthermore, the present invention is not boundby any particular write pole shape as viewed from the ABS plane, andthereby encompasses trapezoidal shapes as well as shapes that have oneor more curved sides including a concave trailing edge as appreciated bythose skilled in the art.

The inventors were motivated to improve the design of a laminated writepole structure since prior art designs that minimize remanentmagnetization and successfully suppress data erasure have a disadvantagein poor writability. Data erasure is a critical issue because a mainpole layer must have a sharp pointed geometry that easily causes dataerasure in adjacent tracks. Typically, a laminated write pole is made ofa plurality of magnetic layers in which adjacent magnetic layers areseparated by a thin non-magnetic spacer. FIGS. 3-5 show simulatedresults using a micromagnetic modeling program based on theLandau-Lifshitz-Gilbert equation for a conventional laminated write polehaving magnetic layers of equal thickness. In FIG. 3, the remanent fieldat the media surface is shown after a write operation inanti-ferromagnetically coupled pole heads made of 1, 2, and 4 magneticlayers as illustrated by curves 60, 61, and 62, respectively. Themagnetostatic interaction or anti-parallel coupling favors oppositedirectional alternate magnetization configurations so the remanent fieldfrom the write pole is effectively reduced as the number of magneticlayers increases. For a certain number of magnetic layers, largeranti-ferromagnetic coupling is more effective in minimizing theremanence. Thus, lamination can reduce remanence by about 10% to 35%compared with a single layer write pole.

Referring to FIG. 4, a graph illustrates a decrease in writability inconventional laminated write poles, particularly near the trailing edge.In this example, a laminated structure with four magnetic layers ofequal thickness has a reduced write field near the +0.2 micron downtrack position (0.05 micron inside from the trailing edge) while aneight layered scheme shows a significant loss in write field across abroad range of down track positions. The data is based on a laminatedstructure having FeCo magnetic layers with 2 nm thick Ta non-magneticspacers where the total write pole thickness is kept at 0.25 microns.

Referring to FIG. 5, the perpendicular write field at the trailing edgeof the write pole is plotted as a function of the spacer thickness forlaminations with a varying number of magnetic layers. As the spacerthickness becomes larger and the number of magnetic layers increases,the write field decreases.

Referring to FIG. 6 a, a schematic illustration is provided to show theflux density distribution 32 in the write pole tip 30 of a single layerwrite pole near the ABS plane 33-33. A similar drawing is shown in FIG.6 b for magnetic flux 32 in a laminated write pole where the thicknessof the magnetic layers 40 a-40 d is essentially constant from leadingedge to trailing edge near the flux return pole 31. Non-magnetic spacers41 a-41 c are also depicted. Flux density in the pole tip is lower forthe conventional laminated structure because total magnetic volume isreduced due to the presence of non-magnetic spacers. In addition, thenon-magnetic spacer has very low flux density and therefore theboundaries of the magnetic layers adjacent to the spacers also have lowflux density. Each magnetic layer effectively operates as an individualthin magnetic layer and flux flow tends to be vertical to the ABS. Fluxdensity in the trailing layer 40 d drops significantly because othermagnetic layers do not provide their flux and this is the main reasonfor poor writability.

In FIG. 7, the overwrite capability is plotted as a function of thenumber of magnetic layers in a laminated write pole with 2 nm thicknon-magnetic spacers and clearly indicates that more lamination leads topoorer overwrite performance.

According to the present invention, various embodiments of laminatedwrite pole structures are provided to overcome the problem of poorwritability caused by a reduction in magnetic flux near the trailingedge of the write pole. The inventors have found that a thick trailingmagnetic layer can compensate for the introduction of non-magneticspacers in a laminated write pole scheme. Neighboring magnetic layersare exchange decoupled or antiferromagnetically coupled (AFC) throughthe thin non-magnetic spacers.

Referring to FIG. 8 a, a view of the write pole 23 of a main pole layerformed within an insulation layer 22 according to the present inventionis seen from an ABS plane. A substrate 20 is provided that may becomprised of AlTiC, for example. The substrate 20 may also be aninsulation layer formed on a top shield (not shown) in a mergedread/write head. In the exemplary embodiment, a RIE resistant layer 21may formed on the substrate 20 by a sputter deposition or physical vapordeposition (PVD) process, for example, and preferably is made of amaterial such as Ru or NiCr that has a high selectivity relative to aninsulating material such as alumina during a subsequent RIE etch thatuses BCl₃, chlorine, and fluorocarbon gases. Alternatively, the writepole 23 and main pole layer may be formed directly on the substrate 20or on a seed layer disposed on the substrate. Above the RIE resistantlayer 21 is an insulation layer 22 wherein a mold shape comprising anopening for the write pole is formed. The insulation layer 22 may becomprised of Al₂O₃ or silicon oxide that is deposited by a PVD process,a sputtering technique, or the like in the same deposition tool as theRIE resistant layer. The insulation layer 22 may also be made of otherdielectric materials known in the art. In an embodiment where the writepole 23 and main pole layer (not shown) are sputter deposited to fillthe mold opening, the insulation layer 22 has a thickness equivalent tothe desired thickness of the main pole layer and a chemical mechanicalpolish (CMP) technique may be employed to planarize the main pole layerincluding write pole 23. Optionally, the main pole layer and write pole23 may be formed by first depositing one or more magnetic layers on thesubstrate 20 with or without an etch stop layer 21. Then a photoresistlayer (not shown) is patterned on the main pole layer material followedby one or more etch steps that define the shape of the write pole 23 andmain pole layer. Thereafter, the photoresist is stripped and theinsulation layer 22 is deposited. A CMP process may be used to make theinsulation layer 22 coplanar with the write pole 23 and main pole layer.

A photoresist patterning and etching sequence for forming a mold in aninsulation layer during a main pole layer fabrication has beenpreviously described in Headway application HT07-005 which is hereinincorporated by reference in its entirety. In one embodiment, a firstphotoresist layer is patterned on an insulation layer and etched to forma rectangular shape that corresponds to the pole section of the mainpole layer. The rectangular shape is transferred through the insulationlayer by a RIE process comprising BCl₃, Cl₂, and a fluorocarbon gas togenerate a trench with beveled sidewalls. Thereafter, the firstphotoresist layer is removed and a second photoresist layer is coated onthe insulation layer and patterned to form a yoke shape opening that ispartially superimposed over the rectangular trench. A second etchprocess involving BCl₃ and Cl₂ may be employed to transfer the yokeshape opening through the insulation layer and form essentially verticalsidewalls in the yoke section of the mold for the main pole layer.Optionally, other double photoresist patterning and etching sequences ora single photoresist patterning and etch process may be used to form amold in the insulation layer 22 for depositing the main pole layercomprising write pole 23. However, a technique is preferred thatproduces essentially vertical sidewalls in the yoke section of the moldand especially adjacent to the neck (not shown) in order to enable amaximum amount of magnetic material volume in the yoke proximate to theneck. A two mask process for forming a mold as previously disclosed bythe inventors in Headway patent application HT07-005 provides anadditional advantage of improving dimensional control of the write poleby minimizing the effect of ABS positioning errors.

In one embodiment of the present invention, the write pole 23 has atrapezoidal shape with sloped sidewalls 23 s wherein the top surface 23t of the write pole has a larger width along the ABS plane than thebottom surface 23 b. Moreover, the sidewalls 23 s are sloped at an angleθ of about 5 to 20 degrees with respect to the plane of the RIEresistant layer 21(and substrate 20). The pole has a beveled shape withan angle θ so that the skew related writing errors can be suppressed.Note that during a write operation, the write pole 23 moves in anegative “z” direction such that the top surface 23 t is the trailingedge. The present invention also anticipates other write pole structuressuch as one where the top surface 23 t has a concave shape that can beformed by performing an etching process on a trapezoidal shape.

In a related Headway patent application, HT07-013. which is hereinincorporated by reference in its entirety, a non-AFC lamination schemeis disclosed that involves an amorphous material layer such as a metaloxide inserted between two high moment layers. One embodiment employsalternating AFC lamination (Ru spacer) and non-AFC lamination tominimize remanence, Hc, and Hk.

Referring to FIG. 8 b, an enlarged view of a portion of the write pole23 in FIG. 8 a is shown on the RIE resistant layer 21. In a firstembodiment, the laminated write pole 23 is comprised of alternatingmagnetic layers 24 a-24 d and non-magnetic spacers 25 a-25 c. Animportant feature is that the trailing magnetic layer 24 d has athickness greater than that of the other magnetic layers 24 a-24 c andpreferably has a thickness that comprises ≧25% of the total thickness ofthe magnetic layers in the write pole 23. Optionally, when the trailingmagnetic layer 24 d has a concave shape (not shown) with a curvedtrailing edge, the volume of the trailing magnetic layer is greater thanthe volume of other magnetic layers 24 a-24 c and is preferably ≧25% ofthe total volume of the magnetic layers 24 a-24 d. The present inventionalso encompasses other embodiments wherein the number of magnetic layersis unequal to 4 but is an integer greater than 1. Moreover, there may bea cap layer (not shown) formed on the uppermost magnetic layer 24 dwhich functions as a CMP stop during fabrication of the main pole layercomprising write pole 23. Preferably, the non-magnetic spacers 25 a-25 chave equal thicknesses but the present invention also anticipates thatone or more of the non-magnetic spacers may have a thickness unequal tothe other non-magnetic spacers. Non-magnetic spacers 25 a-25 c may becomprised of Ru, Rh, Al₂O₃, SiO₂, AlN, Ta, Ti, W, Cr; or NiCr and have athickness in the range of 5 to 100 Angstroms. Magnetic layers 24 a-24 dmay be made of a high moment material such as CoFe, CoFeNi, FeCoN, orFeNi. The movement of the write pole 23 over a magnetic media during awrite operation is in the “−z” direction meaning that the surface ofmagnetic layer 24 d farthest from the RIE resistant layer 21 is thetrailing edge. It should be understood that the trailing edge isadjacent to a trailing shield through a non-magnetic write gap (notshown).

Two embodiments of the present invention are depicted in FIGS. 9 a, 9 b.Note that these drawings represent a top-view (cross-track view) whereinthe trailing edge on the larger magnetic layer 24 d is shown on theright adjacent to the flux return pole 31. Preferably, there is also atrailing shield (not shown) proximate to the trailing edge of magneticlayer 24 d. The write pole 23 moves in the “−z” direction along ABSplane 33-33 during a write operation. Substrate 20, RIE resistant layer21, and a magnetic media layer are not shown in order to simplify thedrawing.

Referring to FIG. 9 a, a first embodiment is shown in which magneticlayers 24 a-24 c have equivalent thickness w which is less than thethickness v of the trailing magnetic layer 24 d. Alternatively, forexamples in which there are “n” magnetic layers where n>1, “n−1” layershave an equivalent thickness and the trailing magnetic layer has alarger thickness than the other magnetic layers. Preferably,non-magnetic spacers 25 a-25 c have an equivalent thickness but thethickness of the non-magnetic spacers may vary within the range of 5 to100 Angstroms as mentioned previously.

Referring to FIG. 9 b, a second embodiment is shown in which magneticlayers 24 a-24 c have a thickness less than v for the trailing magneticlayer 24 d. Moreover, the thickness of the magnetic layers becomesprogressively smaller as the distance from magnetic layer 24 dincreases. For example, the thicknesses a, b, and c, for magnetic layers24 a, 24 b, and 24 c, respectively, have values such that c>b>a.Optionally, for examples where there is a plurality of “n” magneticlayers, the “n−1” layers other than the trailing magnetic layer may eachhave different thicknesses that become progressively smaller withincreasing distance from the trailing magnetic layer. The “n−1”non-magnetic spacers that separate the “n” magnetic layers may have anequivalent thickness or their thicknesses may vary within a range of 5to 100 Angstroms.

Referring to FIG. 9 c, a third embodiment of the present invention isillustrated in which a non-magnetic spacer between the trailing magneticlayer 24 d and the nearest magnetic layer 24 c in preceding embodimentsis replaced by a magnetic spacer 26 made of a soft magnetic materialwhich effectively couples the magnetic moments of the aforementionedmagnetic layers and thereby increases the effective thickness and volumeof the trailing magnetic layer by including the magnetic thickness andvolume of the nearest magnetic layer. A key feature is that thethickness of the trailing magnetic layer 24 d and the nearest magneticlayer 24 c should be greater than that of any of the other magneticlayers 24 a, 24 b. Thus, this embodiment encompasses a configurationwherein all of the magnetic layers 24 a-24 d have an equivalentthickness. However, the third embodiment also anticipates otherconfigurations in which the write pole 23 has a plurality of “n” layerswherein at least two of the magnetic layers have different thicknesses.Preferably, the thickness of the trailing magnetic layer near the fluxreturn pole 31 and that of the magnetic layer nearest to the trailingmagnetic layer are of sufficient magnitude such that their combinedthickness is greater than any of the other magnetic layers.Alternatively, the trailing magnetic layer and the magnetic layernearest to the trailing magnetic layer have a combined volume that isgreater than any of the other magnetic layers. In the third embodiment,the magnetic spacer 26 may be comprised of NiFe, CoNiFe, or a Co basedamorphous material and has a thickness from about 20 to 200 Angstroms.

Referring to FIG. 10, the flux density distribution in the thickertrailing magnetic layer design of the first embodiment is depicted. Animportant feature is that the thicker trailing magnetic layer 24 d has amuch larger flux density 32 compared with the trailing magnetic layer inlaminated layer schemes (FIG. 6 b) where the magnetic layers haveequivalent thickness. Furthermore, in FIG. 10, the flux direction inmagnetic layer 24 d is tilted toward the flux return pole 31 near theABS plane 33-33 thereby substantially improving the head field strengthand profile compared with conventional laminated write poles. In orderto confirm the effect of a thicker trailing magnetic layer, variouslaminated write pole configurations shown in FIGS. 11 a-11 d wereevaluated by a finite element method (FEM) calculation. The ratio of thetrailing magnetic layer 24 d thickness to the total thickness ofmagnetic layers 24 a-24 d changes from ⅙ in FIG. 11 a to ¼ in FIG. 11 bto ⅜ in FIG. 11 c and to ½ in FIG. 11 d. Total thickness in eachconfiguration is fixed at 0.25 microns. Note that the thicknesses ofmagnetic layers 24 a-24 c are equivalent in each configuration butbecome progressively smaller as the trailing magnetic layer 24 d growsin size from configuration (a) to (b) to (c) to (d).

In FIGS. 12 a, 12 b, the calculated perpendicular head field profiles inheads having write pole configurations (a)-(d) are shown. Referring toFIG. 12 b, a close up view of the write pole down-track profiles isdepicted. It is clear that configuration (d) with the thickest trailingmagnetic layer 24 d has the highest write field at the trailing edge(around the +0.2 micron down-track position) as shown in curve 51.Besides a higher write field intensity for curve 51, the head fieldgradient is also improved. Curves 52, 53, and 54 show the write fieldfor configurations (a), (b), and (c), respectively.

Referring to FIG. 13, the perpendicular write field for configurations(a) to (d) in FIGS. 11 a-11 d is plotted as a function of the ratio oftrailing magnetic layer thickness to total magnetic layer thickness. Aratio of 1 along the x-axis represents a single layer write pole. Thecurve in FIG. 13 indicates that a higher ratio provides a larger writefield that starts to saturate around a ratio of 0.4. In other words, ata ratio of 0.5 or greater as in configuration (d), the write field of alaminated scheme according to the present invention is essentially thesame as for a single write pole layer.

Referring to FIG. 14, the laminated pole configurations (a)-(d)represented in FIGS. 11 a-11 d were tested on a perpendicular media andthe resulting overwrite performance is shown as a function of the ratioof trailing magnetic layer 24 d thickness to total magnetic layer 24a-24 d thickness. The results are in agreement with the calculated writefield at the trailing edge (FIG. 13) as the thicker trailing magneticlayer (higher ratio) improves the overwrite capability and theimprovement starts to level off around the 0.4 ratio. Therefore,configuration (d) offers the best advantage in terms of better overwriteand larger write field at the trailing edge for laminated designs andthere is a slight drop off in improvement for configuration (c).

Referring to FIG. 15, transition length is plotted as a function of theratio of trailing magnetic layer 24 d thickness to total magnetic layer24 a-24 d thickness for the laminated write pole configurations in FIGS.11 a-11 d. Since it is well known that transition length correlatesclosely with media signal to noise ratio, the smaller transition lengthat the higher thickness ratio for configuration (d) means an improvedsignal to noise ratio over other laminated write pole configurations.Note that for conventional write pole laminations that have fourmagnetic layers of equivalent thickness, the ratio of 0.25 is expectedto be similar to that of configuration (b) in FIG. 11 b which is clearlyinferior in overwrite performance, transition length, and write fieldmagnitude in the down-track positions to configurations (c) and (d) inFIGS. 11 c, 11 d, respectively, that represent embodiments of thepresent invention.

Thus, the inventors have demonstrated that a thicker trailing magneticlayer in a laminated write pole structure having adjacent magneticlayers antiferromagnetically coupled through a non-magnetic spacerprovides several advantages over prior art configurations whereinmagnetic layers in a laminated scheme have essentially the samethickness. Furthermore, the inventors have disclosed a variation of thefirst embodiment in which the non-magnetic spacer between the trailingmagnetic layer and a neighboring magnetic layer is replaced by amagnetic spacer to couple the magnetic moments in those two magneticlayers and effectively increase the magnetic volume in the trailingmagnetic layer. As a result, the advantages of the second embodiment areanticipated to approximate the benefits in overwrite capability,improved field strength at the down-track positions, and better signalto noise ratio achieved with the first embodiment.

While this invention has been particularly shown and described withreference to, the preferred embodiment thereof, it will be understood bythose skilled in the art that various changes in form and details may bemade without departing from the spirit and scope of this invention.

We claim:
 1. A laminated write pole structure formed on a substrate andalong an air bearing surface (ABS) and consisting of: (a) a plurality of“n” high moment magnetic layers wherein n is at least 4 with acomposition (M) each having a thickness in a direction perpendicular tothe substrate wherein a magnetic layer farthest from the substrate isdefined as the trailing magnetic layer during a write operation and hasa thickness greater than the thickness of any of the other “n−1”magnetic layers, the “n−1” magnetic layers have a progressively smallerthickness wherein the thickness of a magnetic layer decreases as thedistance of the magnetic layer from the trailing magnetic layerincreases and wherein the plurality of high moment magnetic layers guidemagnetic flux to the ABS during a write operation; and (b) “n−1”non-magnetic spacers (S) that are formed in alternating fashion with themagnetic layers to give a [M/S]_(n)M configuration such that there is anon-magnetic spacer that separates neighboring magnetic layers and has athickness that promotes an antiferromagnetic coupling or exchangedecoupling between neighboring magnetic layers.
 2. The laminated writepole structure of claim 1 wherein the magnetic layers are comprised ofCoFe, CoFeNi, FeCoN, or FeNi, and the non-magnetic spacers are comprisedof Ru, Rh, Al₂O₃, SiO₂, AlN, Ta, Ti, W, Cr, or NiCr and have a thicknessbetween about 5 and 100 Angstroms.
 3. The laminated write pole structureof claim 1 wherein the trailing magnetic layer has a thickness ≧25% ofthe total thickness of the plurality of “n” magnetic layers.
 4. Thelaminated write pole structure of claim 1 wherein the trailing magneticlayer has a volume >25% of the total volume of the plurality of “n”magnetic layers.
 5. The laminated write pole structure of claim 1wherein the non-magnetic spacers all have the same thickness.
 6. Alaminated write pole structure formed along an air bearing surface (ABS)and comprised of a stack of layers formed on a substrate, consisting of:(a) a plurality of “n” high moment magnetic layers wherein n is at least4 with a composition (M) each having a thickness in a directionperpendicular to the substrate wherein a magnetic layer farthest fromthe substrate is defined as the trailing magnetic layer during a writeoperation and wherein the plurality of high moment magnetic layers guidemagnetic flux to the ABS during a write operation; (b) “n−2”non-magnetic spacers that are formed in alternating fashion with the“n−1” magnetic layers closest to the substrate such that there is anon-magnetic layer that separates neighboring magnetic layers except forthe trailing magnetic layer and the nearest magnetic layer, each of saidnon-magnetic layers have has a thickness that promotes anantiferromagnetic coupling or exchange decoupling between neighboringmagnetic layers on opposite sides of each of the non-magnetic layers;and (c) a magnetic spacer formed between the trailing magnetic layer andthe magnetic layer nearest to the trailing magnetic layer, said magneticspacer promotes a direct magnetic coupling between the adjacent magneticlayers.
 7. The laminated write pole structure of claim 6 wherein the “n”magnetic layers are comprised of CoFe, CoFeNi, FeCoN, or FeNi and havethe same thickness.
 8. The laminated write pole structure of claim 6wherein the non-magnetic layers are comprised of Ru, Rh, Al₂O₃, SiO₂,AlN, Ta, Ti, W, Cr, or NiCr and have a thickness between about 5 and 100Angstroms.
 9. The laminated write pole structure of claim 6 wherein themagnetic spacer is comprised of NiFe, CoNiFe, or a Co based amorphousmaterial and has a thickness from about 20 to 200 Angstroms.
 10. Amethod of forming a laminated write pole structure along an air bearingsurface (ABS) in a PMR write head, comprising: forming a stack of layerson a substrate, said stack of layers consists of: (a) a plurality of “n”high moment magnetic layers wherein n is at least 4 with a composition(M) each having a thickness in a direction perpendicular to thesubstrate wherein a magnetic layer farthest from the substrate isdefined as the trailing magnetic layer during a write operation and hasa thickness greater than the thickness of any of the other magneticlayers, the “n−1” magnetic layers between the trailing magnetic layerand substrate have a progressively smaller thickness in which thethickness of the magnetic layer decreases as the distance of themagnetic layer from the trailing magnetic layer increases and whereinthe plurality of high moment magnetic layers guide magnetic flux to theABS during a write operation; and (b) “n−1” non-magnetic spacers (S)that are formed in alternating fashion with the magnetic layers to givea [M/S]_(n)M configuration such that there is a non-magnetic spacer thatseparates neighboring magnetic layers and has a thickness that promotesan antiferromagnetic coupling or exchange decoupling between neighboringmagnetic layers.
 11. The method of claim 10 wherein the magnetic layersare comprised of CoFe, CoFeNi, FeCoN, or FeNi and the non-magneticspacers are comprised of Ru, Rh, Al₂O₃, SiO₂, AlN, Ta, Ti, W, Cr, orNiCr and have a thickness between about 5 and 100 Angstroms.
 12. Themethod of claim 10 wherein the trailing magnetic layer has a volume ≧25%of the total volume of the plurality of magnetic layers.
 13. The methodof claim 10 wherein the trailing magnetic layer has a thickness ≧25% ofthe total thickness of the plurality of magnetic layers.
 14. The methodof claim 10 wherein the “n−1” magnetic layers between the trailingmagnetic layer and the substrate have the same thickness.
 15. A methodof forming a laminated write pole structure along an air bearing surface(ABS) in a PMR write head, comprising: forming a stack of layers on asubstrate consisting of: (a) a plurality of “n” high moment magneticlayers wherein n is at least 4 with a composition (M) each having athickness in a direction perpendicular to the substrate wherein amagnetic layer farthest from the substrate is defined as the trailingmagnetic layer during a write operation and wherein the plurality ofhigh moment magnetic layers guide magnetic flux to the ABS during awrite operation; (b) “n−2” non-magnetic spacers that are formed inalternating fashion with the “n−1” magnetic layers closest to thesubstrate such that there is a non-magnetic layer that separatesneighboring magnetic layers except for the trailing magnetic layer andthe nearest magnetic layer, each of said non-magnetic layers have has athickness that promotes an antiferromagnetic coupling or exchangedecoupling between magnetic layers on opposite sides of each of thenon-magnetic layers; and (c) a magnetic spacer formed between thetrailing magnetic layer and the magnetic layer nearest to the trailingmagnetic layer, said magnetic spacer promotes a direct magnetic couplingbetween said trailing magnetic layer and the nearest magnetic layer. 16.The method of claim 15 wherein the “n” magnetic layers are comprised ofCoFe, CoFeNi, FeCoN, or FeNi and have the same thickness.
 17. The methodof claim 15 wherein the non-magnetic layers are comprised of Ru, Rh,Al₂O₃, SiO₂, AlN, Ta, Ti, W, Cr, or NiCr and have a thickness betweenabout 5 and 100 Angstroms.
 18. The method of claim 15 wherein themagnetic spacer is comprised of NiFe, CoNiFe, or a Co based amorphousmaterial and has a thickness from about 20 to 200 Angstroms.